Project Plymouth Valiant Effort Engine Upgrade

If there's one thing Mopar guys all have in common, it's a love of history. We all remember the days when muscle cars ruled the roads, instead of the current regime of under-powered, jelly-bean looking rides that are thrust upon us now. We remember the obnoxious colors, the loud exhausts, and the time when a threat of not being able to get leaded fuel with a 105 octane rating wasn't even a thought. Those are what many consider the "good ole days."

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But many of us seem to selectively forget that our beloved cars of the time never idled very well, were grossly over-cammed, and drank enough fuel to keep a small city driving today. But that's the great thing about memories; they're always about the cool stuff.

Back in the March '10 issue, my ramblings in my Off the Line column hinted about going back to the good ole days. To me, driving an over-cammed engine with no vacuum that won't idle under 1,200 rpm is still cool. While not being able to buy fuel at the local gas station may be a problem, it does add a certain amount to the coolness factor of the car. Anyway, Project Valiant Effort was due for a face lift and personality change, and in the April '10 issue, we handled the face lift by adding a set of Holeshot wheels and Mickey Thompson tires. Now it's time to address the personality.

3/24Before you ever begin to assemble an engine, it's a good idea to chase all of the threads and then give the block a thorough washing.

The Valiant has been a fun car with its pump-gas friendly 360, and the engine is more than adequate when one wants to play. However, we want to take the demeanor of our Valiant from simple cruiser to stupidly cool cruiser. To accomplish this, we looked back to the good ole days and thought about the cars we remember that were running big compression, over carburetion, and cams with enough lift and duration to snap a standard valvespring. Sure, we all know it's overkill, but it left enough of an impression to keep the memory alive, so here we are. We want to relive our youth. We want to remember a time when if we had to choose between a new camshaft and taking our girl to the Prom, we couldn't wait to show our buddies our new bumpstick.

There are a couple of different ways we could approach this engine build. One way would be to try and make every last bit of horsepower possible by using trick parts, and spending a lot of time refining every aspect of the parts and assembly. Lately though, we have been getting a substantial amount of letters from guys who just can't afford all the trick parts and machining and want to see us start doing stuff without getting carried away. So for this build, we're simply going to do only the machining that is required, and then bolt this thing together. In the end, the engine may not make as much power as it could, but with the right parts selection, power will still be respectable-we hope.

4/24When installing the oil galley plugs, don't forget about the one on the back of the lifter galley.....

The Foundation
Knowing that this engine's planned activities will stretch the limits of an "old," seasoned engine block, we felt it necessary to upgrade and started with a Mopar Performance 340 resto block PN 5007552. Yes, using a Mopar resto block will add to the cost, but this non-Siamese bore block (Siamese version is available PN 5153478) is machined to work with all 340 production components, is a brand-new casting made from high-nickel cast iron for added strength (not a thin wall casting), has four-bolt main bearing caps, and a 340 journal size. It also has a thicker pan rail and webbing (like the '70 340 T/A version), a thicker deck surface, and thicker-bore walls in major and minor thrust directions. The block is rough bored at 3.900-inches to allow various bore sizes, from 3.910-inches to 4.080-inches (finish bore and honing required). Deck height is approximately 9.600-inches. The new resto block includes the original 340 production-casting part number with an "M" added at the end to identify the Mopar 340 block. We happened to find a block that had some unusual cylinder scarring and got a good deal on it. The scoring wasn't bad, and when we took it to our machinist (Auto Performance Engines), the bores cleaned up nicely at 4.060-it was 4.040 when we got it.

5/24....It's visible from the distributor hole if you're not sure of the location.

The rotating assembly we're using consists of Mopar Performance's 4.00-inch stroke crankshaft and Eagle's 6.123-inch connecting rods (PNs P5007252 and CRS6123C3D respectively). For pistons, and a lot of the ancillary items we needed, we contacted Summit Racing and ordered a set of Keith Black forged pistons (PN UEM-KB744-060) and Total Seal rings (PN TSR-T3690-65). For those of you keeping track, these pistons are a flat-top design with two valve reliefs. Although we said that we would not be using any tricks to refine the parts we're using, we did balance the assembly. There's no reason to not have these parts balanced.

12/24With a four-bolt main engine block, we also ran into a problem with the Milodon windage tray. On normal two-bolt main blocks, the windage tray fits fine. We had to notch for the main caps. The outer main bolts were replaced with studs during final assembly.

This brings us to the heart of this endeavor, and that's the camshaft. According to believed instructions, a roller cam is not supposed to fit in this new-or any small-block Mopar-without some serious modifications. Since we wanted a camshaft with lobes that look like they had no ramps (read: big), a roller was really the only logical choice for us, but what about this roller-cam stigma? We wanted to find out what cam would best suit our needs, and the best way to do that is to contact a cam manufacturer. We called the tech line at Comp Cams, gave them our specs, and then asked them to make two recommendations-one for a flat tappet design and one for a roller design. Lucky for us, the guys at Comp also let us know that they have just released (as of this writing) a new solid roller-lifter that they said would fit into a small-block Mopar (PN 8043-16). Since they told us they had the lifter issue covered, we had them tell us what camshaft we should use, and waited to hear their numbers.

13/24Lube up the cam and install the timing chain and gears-check. One nice benefit to running a roller cam is that the threat of wiping....

What they suggested was a custom grind cam with .619 and .615-inch lift, and .247 and .280 degrees of duration at .050-inch lift. This cam was ground on a tight 106-degree LSA. Before you guys cry foul and say it's not streetable, we'll let you know when we get it put in the Valiant. Besides, that's what makes this one cool, remember? One last thing to remember when running a roller camshaft is that the factory cast-iron distributor/oil pump drive must be changed to a bronze unit (PN P3690874). Again, we got ours from Summit Racing.

14/24.....a lobe on start-up is all but eliminated. Keeping things simple means that the camshaft was installed at Zero.

Making sure that everything got the required oil, a Milodon oil pan (PN 30936) and a Melling high volume oil pump (PN M72HV) are used.

Top O' This Heap
To seal the cylinder bores, a set of Mopar Performance aluminum cylinder heads (PN P5153849) were used. These heads have a 63cc combustion chamber, 2.02/1.60-inch valves, and valvesprings rated for camshafts up to .575-inch lift. We would need to change the springs for our engine. Replacing the factory springs are a set of Comp's (PN 999-16) valvesprings, which also required some spring pocket-machining, and new retainers. The new springs are a larger 1.55-inch diameter. The retainers are PN 732-16 and use 10-degree valve locks (PN 613-16). For rocker gear, a set of Comp's Pro Magnum rocker arms (PN 1322-16) finish the heads. Since we decided that the engine's parts would simply be bolted on, we did not do any porting on these heads-not even a gasket match. We're sure that power will be down slightly because of this. Our combination of rotating-assembly parts in the block resulted in the pistons sticking .025-inch out of the cylinders, so we knew that an off-the-shelf gasket wasn't going to cut it. The main reason we surmised that reasoning was that if the average head gasket has a compressed thickness of .040-inch, and the pistons stick up .025-inch, that only leaves a margin of .015-inch of room between the cylinder-head face and the piston. We like to have a quench area in the cylinder of about .040-inch so we contacted Cometic Gaskets and ordered up a set of their MLS head gaskets with a compressed thickness of .070-inch (PN H1765070S). This gave us .045-inch of area, and we felt safe with this margin. The rest of the gaskets are also from Cometic (PN PRO1000T). The math showed us a final compression ratio of 11.94:1.

15/24When we started planning our build, Comp Cams was just finishing up the development of their new solid-roller lifters that fit in the Mopar small-block, and require no machining to the block for fitment. It's your choice to tube or bush the lifter bores. Again, it's not required-we verified that with our build.

Now, at the beginning of this reliving-of-our-youth engine build, we mentioned over-carburetion, and nothing screams of over-carburetion like a tunnel ram with dual carburetors. In today's day and age, there really is no logical reason to run a tunnel ram on the street. We're not logical, and we're going to. Anyway, the setup we chose to run is Weiand's Hi-Ram intake (PN 1995), and two Holley 465-cfm vacuum secondary carburetors (PN 0-1848-1). Theoretically, that equals 930 cfm. Not overly overkill, but it'll do. We followed that up with the appropriate linkage and air cleaner assembly (PNs 4023 and 7221 respectively). We're quite certain that we can get more power with a good single-plane intake and single carburetor, but remember, this is an old school build.

16/24Like we said earlier, a standard head gasket wasn't going to cut it in our application, so a pair of Cometic MLS gaskets was chosen for the heads.....

Well, now it's assembled and ready to run-hopefully run. As of this writing, we're getting ready to load it up and hook it to the proverbial lie detector. Tune in later to see if we struck gold with our build, or crapped out.

17/24.....The gasket is .070-inch thick compressed. Cometic gaskets were also used on the rest of the engine.